The invention relates to a vertical column for removing a liquid from a gas.
There are numerous examples in the petroleum and chemical industry where an entrained liquid has to be removed from a gas. The liquid may be entrained in smaller or larger quantities by a flowing gas, in the form of small or large drops, suspended in the form of a mist, as a plug (especially in pipelines), as a foam, etc.
Well known examples are water and liquid hydrocarbons in natural gas, liquid absorption agents in a gas treated with such agents and lubricating oil or crude oil in hydrogen or hydrocarbon gas. An argument for the use of a vertical column for removing liquid from gas is that it occupies little ground area, which is particularly advantageous for offshore application on production platforms, but also in refineries.
Devices of the above mentioned type are widely used in the oil and chemical industry. They may be applied in columns for merely separating gas/liquid mixtures, as well as in columns for contacting liquids and gases for generating an exchange of matter and/or heat between the phases and subsequently separating the phases. The above devices are normally mounted in or over openings in one or more horizontal trays. If the above mentioned devices are applied in columns for contacting liquids and gases, they are provided with mixing chambers having separate liquid and gas inlet means. In said mixing chambers the liquid is atomized in the supplied gas stream so that matter and/or heat between the liquid and gas may be exchanged. The so formed mixture of liquid and gas is supplied to the swirl imparting means of said devices for subsequently separating the liquid from the gas stream.
An example of an apparatus of the above type is described in British patent 1,123,546. This known apparatus comprises a cylindrical wall enclosing an inner space, in which a vane assembly is arranged for separating liquid from a gas/liquid mixture. The cylindrical wall is provided with liquid discharge openings for the withdrawal of the major part of the separated liquid.
Commonly assigned copending patent application Ser. No. 586,482 filed Mar. 5, 1984 which issued on Jan. 28, 1986 as U.S. Pat. No. 4,566,883, describes a further improvement of such a device. It describes an apparatus for separating gas/liquid mixtures comprising an outer vessel having an inlet and separate gas and liquid outlets. A plurality of gas/liquid separating units are mounted in a horizontal tubesheet disposed in the vessel. Each separating unit has a vertical tubular member that defines an inner and outer space with the lower end of the tubular member communicating with the inlet. A swirl vane is mounted in each of the tubular members for imparting a swirl to the gas/liquid mixture to separate the gas and liquid. A primary gas outlet tube extends into each of the tubular members for removing the gas while the liquid is removed through discharge openings in the tubular members. Secondary gas outlets are positioned outside the tubular members while a demister mat is provided for removing any remaining liquid coming from the primary gas outlet tubes.
A problem that arises in the treatment of a given quantity of gas per unit of time if a relatively small diameter column is chosen is that the gas velocity is relatively high, so that there is less time for the liquid separation, and so this proceeds less efficiently.